Washing machines commonly operate on a cyclical programme basis. For example, a typical wash will comprise a wash cycle, a rinse cycle and a spin cycle when the clothes are respectively, washed, rinsed and spin dried. There is normally a draining of liquor between these respective cycles. It is known to provide a pre-wash cycle before the main wash cycle, when it is desired to clean heavily soiled items. Again, there is normally a draining of the pre-wash liquor before dosing of the main wash liquor and execution of the wash cycle.
In the pre-wash, normally the same laundry cleaning product is used as in the main wash. However, it is also known to provide pre-wash compositions to be used in the pre-wash cycle alone, or in combination with some of the main wash composition. These pre-wash products or additives are often formulated so as to attack particularly difficult kinds of soil. When a pre-wash cycle is not used, tough stains may be pre-treated by for example applying undiluted detergent composition to the stained area before laundry is washed in the main wash-cycle. However, the use of a pre-wash cycle or pre-treatment costs extra time and energy. Therefore, there is still a need for an energy efficient laundry cleaning method which optimises the cleaning ability of cost-effective cleaning products.
EP-A-1,375,728 discloses an electric washing machine which uses a drastically reduced amount of detergent but instead electrolysed water, and it is shown in this document that said electrolysed water has an enhanced cleaning capability.
Furthermore, U.S. Pat. No. 5,965,505 discloses a detergent composition containing a heavy metal ion sequestrant and an organic peroxyacid bleaching system, whereby means is provided for delaying the release of said bleach system to a wash system.
We have now discovered that in a single wash cycle, a change in the wash liquor content can optimise the cleaning ability of the wash liquor.
The present invention resides in changing the ionic strength of the wash liquor during the wash cycle. Although not wishing to be bound by theory, it is hypothesised that this influences the interaction between the stain and the surfactant (or a mixture thereof) enabling the removal of a wider variety of stains.